Knoop hardness
The Knoop hardness is measured with a rhombic diamond pyramidal indenter and produces shallow indentations. It is ideal for brittle materials and thin surface layers.
Physical-Chemical Mechanism of Action
The Knoop hardness is measured with a rhombic diamond pyramidal indenter that produces shallow indentations in the metal test piece. This indenter has a special shape with an aspect ratio of 1:7 and imprints a Knoop (rhombic pyramid).
Metallurgical Relevance & Risks in Welding
The Knoop hardness is particularly useful for brittle materials such as steel or titanium because it can accurately measure hardness in thinner surface layers. An excessively high Knoop hardness value can lead to increased brittleness and reduced ductility, posing risks to mechanical strength.
Workshop Practice & Instructions
Use a microhardness tester with a rhombic diamond pyramidal indenter. The test is performed under a 10x-50x magnifier. A typical Knoop hardness value for steel is between 30 and 40 HRC (Rockwell C scale). For unusually high or low values, further investigations into the material structure and deformation should be carried out.